Interconnecting Electronic Mail Systems

Among the technologies that continue to shape patterns of personal communication, one of the most important is the electronic mail system. Various forms of this news communication medium are already being used in businesses, and with the advent of home computing and widespread personal computer networks, electronic mail, like the telephone before it, will evolve into a unixersal facility. But before we can make this goal a realitv, we need a wav to interconnect the many existing and future electronic mail systems to form a larger facility that allows universal message exchange. What exactly is "electronic mail"? A variety of systems use the term, but the system wve feel best represents a true electronic mail system is the computerbased message system. A CBMS prox ides buffered communication among groups of individual users-as opposed to systems like Telex, which provide direct communication between pairs of terminals. A typical CBMS allows a single message to be addressed to many recipients, and often includes facilities such as distribution lists to ease such usage. It also tends to emphasize interactive access for submitting and delivering messages, in contrast with systems like the US Postal Service's Ecom, which emphasizes off-line interaction, such as hard-copy delivery. In short, a CBMS provides many of the facilities of a conventional (nonelectronic) mail or memo distribution system, but with vastly increased speed and consenience. Existing electronic mail systems exhibit a xariety of implementation approaches. The earliest mail facilities were provided as added-value application software on general-purpose timesharing systems, and this approch is still common. Single-purpose machines dedicated to providing electronic mail are also common, particularly among serx ice companies providing dial-in access to manv customers. Over the last decade, progress in distributed computing has produced several multimachine mail systems, providing terminal users with a unified mail system spanning multiple computers. More recently, the advent of personal computers has led to the development of mail servers machines that are accessed not by users themselves, but by the users' personal computers using appropriate communication protocols. In addition to these basic structural differences, the various existing mail systems also display differing solutions to many other design problems. Message formats, user naming conventions, command languages, filing facilities and any number of other areas have been addressed by existing mail systems in a variety of idiosyncratic ways. As a result, the various systems, while similar in their total functionality, are very different from each other in detail. Given the variety of electronic mail systems in existence, interconnection is the key to a unified network. Electronic mail and internetworking are important areas of research and development in their own right, so their convergence-the interconnection of electronic mail systems is doubly important. For electronic mail, internetworking is vital because of the critical mass effect; that is, how effective an electronic mail system is depends primarily on how many people it can reach. Since many potential correspondents will, in practice, be users of different mail systems, interconnection is vital to maximum utility. For internetworking, electronic mail provides a particularly important communication paradigm, fulfilling